Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from `text-mode.el' that illustrate many of the conventions listed above:
;; Create mode-specific tables. (defvar text-mode-syntax-table nil "Syntax table used while in text mode.") (if text-mode-syntax-table () ; Do not change the table if it is already set up. (setq text-mode-syntax-table (make-syntax-table)) (modify-syntax-entry ?\" ". " text-mode-syntax-table) (modify-syntax-entry ?\\ ". " text-mode-syntax-table) (modify-syntax-entry ?' "w " text-mode-syntax-table)) (defvar text-mode-abbrev-table nil "Abbrev table used while in text mode.") (define-abbrev-table 'text-mode-abbrev-table ()) (defvar text-mode-map nil) ; Create a mode-specific keymap. (if text-mode-map () ; Do not change the keymap if it is already set up. (setq text-mode-map (make-sparse-keymap)) (define-key text-mode-map "\t" 'tab-to-tab-stop) (define-key text-mode-map "\es" 'center-line) (define-key text-mode-map "\eS" 'center-paragraph))
Here is the complete major mode function definition for Text mode:
(defun text-mode ()
"Major mode for editing text intended for humans to read.
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map) ; This provides the local keymap.
(setq mode-name "Text") ; This name goes into the mode line.
(setq major-mode 'text-mode) ; This is how describe-mode
; finds the doc string to print.
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(run-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from `lisp-mode.el' that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table
; if it is already set.
(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))
;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is 48
in the ASCII character set.)
(while (< i ?0)
(modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
(setq i (1+ i)))
...
;; Set the syntax for other characters.
(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
...
(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
...))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:
(defun lisp-mode-variables (lisp-syntax) ;; Thelisp-syntax
argument isnil
in Emacs Lisp mode, ;; andt
in the other two Lisp modes. (cond (lisp-syntax (if (not lisp-mode-syntax-table) ;; The Emacs Lisp mode syntax table always exists, but ;; the Lisp Mode syntax table is created the first time a ;; mode that needs it is called. This is to save space. (progn (setq lisp-mode-syntax-table (copy-syntax-table emacs-lisp-mode-syntax-table)) ;; Change some entries for Lisp mode. (modify-syntax-entry ?\| "\" " lisp-mode-syntax-table) (modify-syntax-entry ?\[ "_ " lisp-mode-syntax-table) (modify-syntax-entry ?\] "_ " lisp-mode-syntax-table))) (set-syntax-table lisp-mode-syntax-table))) (setq local-abbrev-table lisp-mode-abbrev-table) ...)
Functions such as forward-paragraph
use the value of the
paragraph-start
variable. Since Lisp code is different from
ordinary text, the paragraph-start
variable needs to be set
specially to handle Lisp. Also, comments are indented in a special
fashion in Lisp and the Lisp modes need their own mode-specific
comment-indent-function
. The code to set these variables is the
rest of lisp-mode-variables
.
(make-local-variable 'paragraph-start)
;; Having `^' is not clean, but page-delimiter
;; has them too, and removing those is a pain.
(setq paragraph-start (concat "^$\\|" page-delimiter))
...
(make-local-variable 'comment-indent-function)
(setq comment-indent-function 'lisp-comment-indent))
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-l to run-lisp
, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following function adds these common commands to a given
keymap.
(defun lisp-mode-commands (map) (define-key map "\e\C-q" 'indent-sexp) (define-key map "\177" 'backward-delete-char-untabify) (define-key map "\t" 'lisp-indent-line))
Here is an example of using lisp-mode-commands
to initialize a
keymap, as part of the code for Emacs Lisp mode. First we declare a
variable with defvar
to hold the mode-specific keymap. When this
defvar
executes, it sets the variable to nil
if it was
void. Then we set up the keymap if the variable is nil
.
This code avoids changing the keymap or the variable if it is already set up. This lets the user customize the keymap.
(defvar emacs-lisp-mode-map () "") (if emacs-lisp-mode-map () (setq emacs-lisp-mode-map (make-sparse-keymap)) (define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun) (lisp-mode-commands emacs-lisp-mode-map))
Finally, here is the complete major mode function definition for Emacs Lisp mode.
(defun emacs-lisp-mode ()
"Major mode for editing Lisp code to run in Emacs.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{emacs-lisp-mode-map}
Entry to this mode runs the hook `emacs-lisp-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map emacs-lisp-mode-map) ; This provides the local keymap.
(set-syntax-table emacs-lisp-mode-syntax-table)
(setq major-mode 'emacs-lisp-mode) ; This is how describe-mode
; finds out what to describe.
(setq mode-name "Emacs-Lisp") ; This goes into the mode line.
(lisp-mode-variables nil) ; This defines various variables.
(run-hooks 'emacs-lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
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